One of the issues regarding vehicles having a fuel cell or hydrogen powered engine is the refilling time of the hydrogen stored onboard the vehicle. In compressed gas hydrogen storage systems, the transfer of high pressure gas from the filling station gas supply to an empty tank onboard a vehicle results in the conversion of the high enthalpy of the gas into heat in the tank as it fills causing the temperature of the stored gas and the onboard tank to rise significantly.
When a gas fills an initially evacuated tank, the gas conducts heat to the tank walls. The actual temperature increase of the gas and the tank depends on the amount of gas put into the tank and the heat capacity of the tank itself. The result of this increase in temperature of the gas and tank system is to reduce the amount of gas that can be put into the tank at the pressure supplied by the filling station gas supply. Therefore, a complete filling of the onboard tank requires active heat management to extract the heat of filling from the onboard tank. Without active heat management, the filling time would be unacceptably long due to slow passive dissipation of heat from the onboard tank to the surrounding environment.
It is known in the art to manage heat of onboard compressed tanks by (1) active cooling of the tank, which requires additional onboard equipment that adds cost and weight to the vehicle; (2) significant active cooling of the hydrogen gas prior to filling; and (3) careful monitoring of the temperature of a slowly filling tank and correspondingly controlling the pressure and flow of the filling hydrogen gas to optimize the heat load in the tank to match the active or passive heat management of the tank. An improved method of filling a compressed hydrogen gas storage tank on a vehicle is needed.